An inkjet recording method is a method of performing printing by jetting and attaching small liquid drops of ink to a recording medium such as paper, as well-known in the art. By this printing method, it is possible to conveniently print a high-resolution and high-quality image at a high speed with an inexpensive apparatus, and particularly, in color printing, a technical development for the printing method has been recently performed as an image forming method which may replace photographs.
When a color image is formed using an inkjet recording method, it is common to use at least a yellow ink, a magenta ink, a cyan ink and a black ink. In the related art, water-based inks have been mainly used as these inkjet inks in terms of safety, such as malodor and hazards associated with firefighting. These inks are required to fall within suitable ranges in physical property values such as viscosity and surface tension, to be excellent in storage stability and prevent clogging of a nozzle, to impart a recording image at a high concentration, and to be excellent in light fastness, ozone resistance, water resistance and moisture resistance.
Such a performance is mostly satisfied by using a water-based ink containing water or a mixture solution of water and a water-soluble organic solvent as a main solvent, but since color tone, saturation, light fastness, ozone resistance, water resistance, moisture resistance and the like are influenced considerably by coloring agents, various dyes have been studied in the related art.
In particular, in a color recording method using a plurality of color inks, uniform characteristics are required for all the constituting inks. Among them, a magenta dye has a problem in that discoloration or change in color tone by ozone or light (sunlight, fluorescent light and the like) occurs significantly, as compared to the other dyes (a cyan dye and a yellow dye). Accordingly, when ozone resistance or light fastness of the magenta ink is inferior to that of the other inks, discoloration of the magenta ink causes the color tone of the overall image of printed matters to be changed, resulting in deteriorating the quality.
In the related art, an acidic dye having good chromogentic property and high water solubility, for example, C. I. Acid Red 52, 249 and 289, is known as a magenta dye for inkjet, but when such a dye is used alone, clogging of a nozzle hardly occurs due to the high water solubility, but the performances of the ozone resistance, and light fastness are very low.
Patent Document 1 discloses a water-based ink for inkjet recording, which contains a dye composed of C.I. Acid Red 289 that is a xanthene derivative, or a xanthene derivative having more sulfo groups than C.I. Acid Red 289.
Further, as the magenta dye for inkjet, an azo-based dye is also known. Patent Document 2 discloses an azo colorant having a specific structure.
In addition, as an azo colorant having a good hue, Patent Document 3 discloses a coloring composition having a good hue and fastness to light and ozone by using a heteryl azo dye having a specific substituent.
Furthermore, Patent Documents 4 and 5 disclose that a magenta dye having a good hue and fastness to light, ozone and humidity is provided by a specific compound having an anthrapyridone skeleton.
Patent Document 6 discloses an ink in which a xanthene-based compound and an azo-based compound are used in combination.